Weight loss for a 13 years old? My mother won't allow me to start exercise or go on a diet

I am 13 years old and i cant loose weight i am 60kg ap, and i wanna be at least 50kg my mum doesnt allow me to go out side and excercise nor does she allow me to go on diets. I know that it is bad to starve yourself or make yourself vommit so i wont try to do that but how can i loose weight.